Seismic behavior of concrete filled steel tubular arch structures

Shaking table tests of a 1:10 scale arch model performed to investigate the seismic behavior and resistance of concrete filled steel tubular (CFT) arch structures are described in this paper. The El-Centro record and Shanghai artificial wave were adopted as the input excitation. The entire test process can be divided into three stages depending on the lateral brace configurations, i.e., fully (five) braced, two braces removed, and all braces removed. A total of 46 tests, starting from the elastic state to failure condition, have been conducted. The natural vibration frequencies, responses of acceleration, displacement and strain were measured. From the test results, it is demonstrated that the CFT arch structures are capable of resisting severe ground motions and that CFT arches offer a credible alternative to reinforced concrete arches, especially in regions of high seismic intensity.

Improving the design of reinforcing frames by simulating the arch and peltate venation structures

Based on the analyses on arch and peltate venation structures, the design of reinforcing frames was improved. First, distribution rules of the arch structure were summarized. According to the load condition and the structure of the frame, a mechanical model of arch structure was devel- oped, and two solutions for the model were analyzed and compared with each other. Through the a- nalysis, application rules of arch structure for improving the design were obtained. Then, distribu- tion rules of peltate venation structure were summarized. By using the same method, application rules of peltate venation structure for improving the design were also obtained. Finally, mechanical problem of the frame was described, and rib arrangement of the frame was redesigned. A parameter optimization for the widths of ribs in bionic arrangement was also carried out to accomplish the im- proving design. Comparison between bionic and conventional reinforcing frames shows that the weight is reduced by as much as 15.3%.

Reasonable location of stopping line in close‑distance underlying coal seam and partition support of large cross‑section roadway

Close-distance coal seams are widely distributed over China,and the coal pillars left by the overlying coal seams afect the retracement channel of the underlying coal seam in the stopping stage.Based on the engineering background of close-distance seam mining in a coal mine,the reasonable position of the underlying coal seam's stopping line and the support method of the large section roadway during stopping are investigated using feld measurements,similar simulation experiments,and numerical simulations.There are three types of location relationships between the stopping line of the underlying coal seam and the stopping line of the overlying coal seam:"externally staggered with the upper stopping line"(ESUL,stops mining under the overlying goaf),"overlapped with upper stopping line"(OUL),and"internally staggered with the upper stopping line"(ISUL,ISUL-SD for shorter internal staggered distances,ISUL-LD for longer ones).There are diferent stress arch structures in the overlying strata of the above three positions,and the stress arch evolution process exists in the process of ESUL→OUL→ISUL-SD→ISUL-LD:a front and rear double stress arch structure→the front arch gradually decreases→the front arch dies out,and the double arch synthesizes the single arch→the single-arch range expands→the nested double arch.The relationship between the stress arch structure and the position of the stopping line is evaluated as follows:(1)ESUL:the stress concentration in the roof plate of the retracement channel of the underlying coal seam is the highest,because the overburden block of the extensive collapse zone acts directly on the roof plate of the retracement channel,resulting in relative difculties in roof support.(2)OUL:although the retracement channel roof pressure is minimal,the overlying rock structure has the potential for rotation or slippage instability.(3)ISUL-SD:the pressure on the roof of the retracement channel is small and the overburden structure is stable,which is conducive to the safe retraction of the support and not limited by the width of the end-mining coal pillar.(4)ISUL-LD:it is basically the same as the condition of stopping under the non-goaf;however,it has a limitation on the width of the end-mining coal pillar.The location of the stopping line is selected as ISUL-SD,and the retraction process of the self-excavating retraction channel was adopted.A partition asymmetric support scheme which is proven by feld practice is proposed,through a comprehensive analysis of the pre-stress feld simulation of the support scheme,based on the diferent control requirements of the roof above the support and the roof of the retracement channel in the stopping area.This method realizes safe and smooth withdrawal of the support.

ARCH STRUCTURE OF TRABECULAE OF THE UPPER FEMORAL END AND ITS BIOMECHANICAL SIGNIFICANCE IN HIP FRACTURES

We studied ultrastructurally the cancellons bone tissues of the upper femoral ends, collected from 12 patients undergoing endoprostbesis replacement for fractures of the femoral neck and from 7 fresh cadavers. The bone tissues were composed of meshwork of trabeculae, that constituted tier upon tier of anisotropic arch structures of different diameters and sizes. The arch structures of the cancellous bone tissues in the femoral heads assumed round or roundish configurations, whereas those of the femoral head-neck junctions revealed oval outlines and those of the femoral necks showed narrow oval profiles. The fine structures of the trabecnlae in the femoral head could be divided into superficial zone, central zone, and transitional zone. Under weight-bearing, the central zone suited to sustain the load, while the superficial zone could produce elastic deformation lest fracture of the trabecaulae should ensue. The long axes of the oval arch structures of the femoral head-neck junction and the narrow oval arch structures of the femoral neck coincided with those of the femoral neck, thereby facilitating weight-bearing under physiological conditions. However, external violence in the form of either adduction or abduction force would act in a horizontal direction on the long axes of the oval and narrow oval arches so as to produce subcapital or transverse fracture of the femur in the aged.

Effect of vacuum degree and aeration rate on sludge dewatering behavior with the aeration-vacuum method

Due to large-scale dredging operations, a large amount of sludge is inevitably produced. Large areas of land are occupied when the dredged sludge is discarded in the disposal site as waste material. The sludge dewatering with aeration-vacuum (SDAV) method is suit for treating the sludge with high water content and high clay content in the disposal site. The water in the sludge can be discharged out. The volume of the sludge can be reduced quickly, and the recycling of the land can be accelerated by this method. Most importantly, this technique is an efficient way to deal with clogging problems when pumping water from high water content, high clay content dredged sludge. Vacuum degree range tests, the aeration rate range tests, and the influencing factors of sludge dewatering behavior tests were conducted with a self-developed SDAV model test device. Sludge samples were taken from the South-to-North Water Diversion East Line Project in Huai’an White-Horse Lake disposal site, Jiangsu Province, China. The optimal range of vacuum degree and aeration rate were obtained through the test results, and the mechanisms for how the two factors work and how they affect the sludge dewatering behavior were analyzed. The suitable vacuum degree range in SDAV is below 50 kPa, and the suitable aeration rate is about 1.0 m3/h. The low-vacuum degree contributes to reduce the ad-sorption effect of micro-channels on soil particles in filter material and to maintain the arch structures. Aeration has the effects of expansion, disturbance, changing Reynolds number, and dynamic sieve separating. The pump quantity of water per meter of filter tube (m) has different change rules as the vacuum degree changes under different aeration rates. The reason is that the formed arch structures’ conformation and permeability differ greatly under different combined-conditions of vacuum degree and aeration rate. The optimal combined-condition for dewatering the sludge is 35 kPa with 1.0 m3/h.